Gravity constant moved into constants.rb, camera can now report what it is looking at, entity has knowledge of camera now, AABB tree search can now use either BoundingBox or Ray colliders

lib/constants.rb

@@ -8,4 +8,9 @@ class IMICFPS
 
   # Objects exported from blender using the default or meter object scale will be close to 1 GL unit
   MODEL_METER_SCALE = 1.0
+
+  # Earth
+  GRAVITY = 9.8 # m/s
+  # Moon
+  # GRAVITY = 1.625 # m/s
 end